1. Field of the Invention
The present invention relates generally to an apparatus and method for communicating control information in a Broadband Wireless Access (BWA) system, and in particular, to an apparatus and method for periodically communicating unchangeable control information in a BWA system.
2. Description of the Related Art
A number of radio communication technologies have been suggested as a candidate for rapid mobile communications. Among the suggested technologies, an Orthogonal Frequency Division Multiplexing (OFDM) scheme is the most dominant next-generation radio communication technology. In the future, it is anticipated that the OFDM technology will be adopted to most of the radio communication technologies. Wireless Metropolitan Area Network (WMAN) of Institute of Electrical and Electronics Engineers (IEEE) 802.16, which is called the 3.5G technology, is adopting the OFDM technology as the standard.
To effectively and freely allocate uplink/downlink in a OFDM based Broadband Wireless Access (BWA) system, a Base Station (BS) transmits information indicative of uplink/downlink resource allocation of the uplink/downlink in every frame. In IEEE 802.16 systems, a (MAP message is used to carry this information.
FIG. 1 illustrates a typical frame structure of the IEEE 802.16 system.
The frame of FIG. 1 includes a DownLink (DL) frame and an UpLink (UL) frame. The DL frame carries data from BS to Mobile Stations (MSs). The UL frame carries data from MSs to BS in designated regions.
The DL frame includes a preamble, a Frame Control Header (FCH), a DL MAP, a UL MAP, and DL data bursts. The UL frame is divided largely to a control region and a UL data burst region. The DL preamble is used for an initial synchronization acquisition and a cell search of the MS. The FCH contains information indicative of a basic structure of the frame. The DL MAP contains information indicative of the DL data burst regions. The UL MAP contains information indicative of the structure of the UL frame.
The control region of the UL frame includes a ranging region, a Channel Quality Information CHannel (CQICH) region, an ACKnowledgment Channel (ACKCH) region, and a sounding region. The ranging region, in which the MS can upload codes without the allocation from the BS, includes an initial ranging region and a periodic ranging region. The ranging region is used to perform a network initial access, request a handoff, or request a resource allocation. CQICH region is used for MS to report of DL channel condition. ACKCH region is used to report of whether the DL data bursts are successively received. The sounding region carries a sounding signal for a UL channel estimation.
In general, the frame structure is defined by the BS. The MS can acquire frame structure and allocation information by receiving DL MAP and UL MAP of the DL frame from the BS in every frame.
As above, while the frame structure is dynamically changed according to the specification, it scarcely changes in the actual system and every frame retains the same structure. Usually, the UL control region such as the ranging region, the CQICH region, and the ACKCH region in FIG. 1 is not changed. Accordingly, it is considerable loss in terms of the efficiency of the resource utilization to transmit the allocation information relating to this fixed region in every frame.
In practice, in an IEEE 802.16e system, the amount of resources used to describe the UL control region is 212 bits in total: 104 bits of the ranging region, 52 bits of the CQICH region, and 56 bits of the ACKCH region. The 212-bit information amount corresponds to two OFDM symbols in size when it is encoded at 1/12. Typically, when MAP information occupies 6-10 OFDM symbols, it can be said that the allocation information of the UL control region occupies more than 20% in the MAP information. Since the conventional system cannot utilize the region occupied by the allocation information of the UL control region as the UL data burst region, a loss of about 10% occurs in the system capacity.
As discussed above, what is needed is a method for effectively transmitting allocation information relating to the unchangeable region (UL control region) in the frame structure.